THE increase in the acreage of maize being grown in the UK, more latterly as a result of feedstock demand from the growing number of anaerobic digestion (AD) plants, has brought with it increasing disease pressure. Teresa Rush reports.

﻿For the first time growers have a fully approved fungicide option for control of the two most common and increasingly prevalent diseases in maize. This follows the launch of Propiconazole+azoxystrobin co-formulation Quilt Xcel from Syngenta.

Speaking at the launch of the new fungicide, NIAB TAG plant pathologist Dr Jane Thomas outlined the threat to yield posed by the two main foliar diseases – maize eyespot (Kabatiella zeae, now known as Aureobasidium zeae) and northern corn leaf blight (Helminthosporium).

Early die-back of maize as a result of these diseases can severely affect yields of forage maize and feedstock for biogas production.

Yield losses as a result of foliar disease can reach 50 per cent, says Syngenta, and there is anecdotal evidence of virtually complete crop losses following severe outbreaks of eyespot in commercial crops in recent seasons. Crop quality can also be affected.

Fungicide control options have until now been limited to flusilazole – now withdrawn (stocks must be used by October 12, 2014) – and pyraclostrobin under an Extension of Authorisation for Minor Use (EAMU).

In addition, maize breeders are working to provide varietal resistance, says Dr Thomas.

Syngenta maize portfolio manager Wouter Keppens says eyespot is the most damaging leaf disease of maize crops when conditions are right for its development.

He says: “In cool and wet seasons, infection can cut the maize growing season by several weeks at a time when plants should be putting on the maximum cob grain fill.”

UK experience of the disease in recent seasons – 2011 and 2012 – has demonstrated the epidemic potential of the disease, with crops being harvested early and warnings of limited forage supply and quality.

Mr Keppens says: “In the UK, eyespot most typically occurs in the South and West, but can occur anywhere during wet weather. First infection can occur from early second leaf growth stage but is not usually seen until later in the season.”

Northern leaf blight was first identified in the UK in 2008 but with climatic conditions favourable to its development and the increase in industrial maize cropping, its incidence is expected to increase in coming years.

He says: “Wet soils and damp leaf surfaces in humid conditions appear most conductive to rapid infection. Initial spots can spread by more than 1cm in just 24 hours, leading to rapid leaf loss.”

While leaf blight itself does not give rise to harmful mycotoxins, research has shown infections can make plants more susceptible to other fungi capable of producing mycotoxins, including fusarium and aspergillus, Mr Keppens adds.

According to Maize Growers Association agronomist Simon Draper, applying a fungicide to maize provides some insurance against crop loss.

He says: “For a big livestock producer who does not have sufficient feedstocks elsewhere, I would suggest it is an insurance policy.”

But the decision to use one is largely weather-driven. “In a hot, dry year, I would advise you do not go [with a fungicide].”

Conversely, in a high disease pressure season, two fungicides may be required. “If it is a cold, wet June, we will probably spray,” says Mr Draper.

With the aim being to protect big leaves at the top of the maize canopy, advice is to leave fungicide applications as late as possible, which will be determined by the clearance of the sprayer.

Mr Draper says: “My recommendation is to spray as late as you can as you will need the persistence. The last possible time you can get through the crop is the time to go.”

His advice is echoed by Syngenta maize field technical manager Simon Roberts.

Mr Roberts says: “For best results, application should be as late as possible through the flowering period to minimise the impact of late occurring diseases.

“If early symptoms are identified, however, early intervention will protect uninfected plants and prevent further spread of leaf diseases.

“In practice, application timing is going to be dictated by the physical ability to spray in tall plants as the crop grows.”

In 2013, only about 5 per cent of the maize crop received a fungicide application, while in 2012 the figure was probably 70-80 per cent, says Mr Draper.